Radio observations of massive stars in the Galactic centre: The Quintuplet cluster

¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: gallego@iaa.es
² Centro de Astrobiología (CSIC/INTA), Ctra. de Ajalvir Km. 4, 28850 Torrejón de Ardoz, Madrid, Spain
³ CIERA, Department of Physics and Astronomy Northwestern University, Evanston, IL 60208, USA
⁴ Max-Planck-Institut für Astronomie, Königstuhl 17, Heidelberg 69 117, Germany

Received: 28 July 2021
Accepted: 13 December 2021

Abstract

We present high-angular-resolution radio continuum observations of the Quintuplet cluster, one of the most emblematic massive clusters in the Galactic centre. Data were acquired in two epochs and at 6 and 10 GHz with the Karl G. Jansky Very Large Array. With this work we have quadrupled the number of known radio stars in the cluster. Even though the uncertainty of the measured spectral indices is relatively high, we tentatively classify the 30 detected stars. Eleven have spectral indices consistent with thermal emission from ionised stellar winds, ten have flat to inverted spectral indices indicative of non-thermal emission arising in colliding winds in binaries, and the nine remaining sources cannot be easily classified because of large uncertainties or extremely positive values of the spectral index. The mean mass-loss rate estimated for Wolf-Rayet stars agrees with previous work. Regarding variability, remarkably we find a significantly higher fraction of variable stars in the Quintuplet cluster (∼30%) than in the Arches cluster (< 15%), probably because the Quintuplet cluster is older. Our determined stellar wind mass-loss rates are in good agreement with theoretical models. Finally, we show that the radio luminosity function can be used as a tool to constrain the age and the mass function of a cluster.